A
hub motor comes laced into a standard bicycle wheel. Just swap out the
tire and tube from your normal wheel, and drop the hub motor into your
bike! Direct drive hub motors are typically three pole single speed
brushless permanent magnet DC motors. They are super reliable and can
travel thousands of miles with zero maintenance. The most popular hubs
can be had for as little as $200, and the biggest x5 hubs can be as much
as $500.

Controller:

The
controller is the magic little box that allows the raw copper, magnets,
and electrons in the motor to function effecienctly and precisely.
These are often zip tied to the bike some where it can get air flow. You
have lots of options for controllers. They range from low powered $50
units all the way up to motorcycle powered $1k monsters. You can get a
decent USB programmable, regenerative braking, Infenion controller for
around $100

Throttle and ebrake:

Throttles
obviously make the motor go. Ebrakes are normal bicycle brake levers
with an on/off sensor. This shuts down the motor, and triggers regen
braking. There are several options for throttles, but only one style of
ebrake lever.

Torque arm:

A
torque arm reinforces the drop out of the bicycle frame. Bicycle are
built to withstand extreme downward force on the dropouts, but not a
rotational force from the axle of a hub motor. Torque arms are essential
for a safe ebike build. There are several varieties. For high powered
bikes it's best to build your own.

Battery:

More
than any other part of the bike, the battery will define how fast and
how far you can go. A trouble free, light weight, and long lasting
battery pack is the key to a satisfying and successful ebike build. The
plug and play options offer a great value for those that just want a
worry free bike, but for a truly powerful bike you'll need to build your
own battery pack. You can spend anywhere between $100 and $1000 for a
good battery pack.

Ebike kit:

A
kit is a great choice for a first bike. They include components that
work well together, and can be significantly cheaper than buying
separately. Typically they include everything excluding the battery!Pricing can range from $250 for a kit direct from China to $500 for a quality kit from an American retailer.

So you want to build an ebike?

Common bike builds: There are lots of options available. Get a feel for what type of bike suits your needs.